Tyre for a vehicle wheel including a tread-band pattern

ABSTRACT

A tire for a vehicle wheel includes a tread band. The tread band includes a pattern, including at least two circumferential portions, an elongated ridge, and at least two shoulder blocks. The at least two circumferential portions are disposed in axial side-by-side relationship. At least one of the circumferential portions includes a first geometric module repeated along a circumferential extension direction of the tire. The elongated ridge is bounded by two grooves oblique to the circumferential extension direction and is divided into a plurality of intermediate blocks with respect to an axial extension direction of the tread band. The intermediate blocks are bounded by a plurality of cuts substantially transverse to the elongated ridge. The at least two shoulder blocks are associated with the elongated ridge, are circumferentially aligned along a side edge of the tread band, and are bounded by grooves oriented substantially transversely to the circumferential extension direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of pending application Ser. No. 10/533,927, filedDec. 2, 2005, which is a national stage entry of InternationalApplication No. PCT/IT02/000814, filed Dec. 19, 2002, both of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a tyre for vehicle wheels.

In more detail, the invention concerns a tyre of the winter type forhigh performance and ultra high performance cars, i.e. cars providedwith particular performance qualities and generally having a rear-wheeldrive.

Description of the Related Art

By winter tyre it is intended a tyre provided with a tread band suitablefor running on surfaces of reduced compactness in particularsnow-covered roadways.

Tyres having the above qualities are usually required to possess,together with optimal features in terms of traction power, braking andhandling on a snow-covered roadway, a good behaviour on dry and wetroads and a satisfactory resistance to wear. Noiseless running alsohelps in elevating or worsening the qualitative evaluation of a wintertyre.

Usually, the above mentioned behavioural and operational features aredetermined through formation in the tread band of appropriatecircumferential and transverse grooves suitably sized and oriented,which grooves give rise to creation of blocks usually aligned in rowsdisposed consecutively in side by side relationship and extendingcircumferentially of the tyre itself.

In addition, of decisive importance as regards the behavioural runningfeatures of a car on a snow-covered roadway is the presence of anappropriate lamelliform arrangement of cuts in the blocks, i.e. a thickseries of narrow cuts disposed consecutively in side by siderelationship in a circumferential direction and oriented substantiallytransversely with respect to the rolling direction. The task of thesenarrow cuts, which are currently referred to as sipes, is substantiallythat of effectively collecting and retaining the snow, since friction ofsnow against snow is known to be greater than rubber-on-snow friction.

In the international patent, application WO 02/068222 in the name of thesame Applicant it is described a winter tyre for vehicle wheelscomprising a tread band provided with three circumferential grooves anda plurality of transverse grooves that together delimit fourcircumferential rows of blocks: two axially external shoulder rows andtwo central rows disposed to the sides of the equatorial plane of thetyre. The transverse grooves converge to the equatorial plane towards apredetermined tyre-rolling direction. On the tread band, each transversegroove belonging to the central rows is provided with an enlarged areain its section having an essentially circular profile, the function ofwhich is to entrap snow. In addition, for obtaining rolling with lessnoise on dry roads as well, each transverse edge of the blocks comprisesat least two successive curvilinear portions. These curvilinear portionsare differently shaped and have opposite bends in the two portions tomitigate noise generated by the impact of the blocks when the tyre isrolling on the ground.

The Applicant has perceived the increasing requirement of ensuring morehandling on snow-covered roadways to all motor-vehicles and above all tothose of the above mentioned high performance type, while at the sametime affording more safety and comfort on dry and wet roads.

In fact many automobile houses during their winter tests have begun toregularly carry out behavioural tests on snow, beside the traditionalacceleration and braking tests.

These tests are subjective behavioural tests and consist in the tyrebeing run on a mixed roadway, characterised by straight stretches andbends to be taken at different speeds, as well as by uphill and downhillportions, on the basis of which a test driver gives his/her opinion ondifferent car handling parameters.

SUMMARY OF THE INVENTION

In this connection the Applicant has found that the winter tyres of theknown art have a side (lateral) grip on snow-covered roadways that isnot quite satisfactory. This phenomenon, present on both the car axles,is more marked on the driving wheels and is highlighted to a greaterdegree on rear-wheel drive cars provided with engines of high power. Infact, to ensure high performance on dry roadways, the cars of this typeusually have low-section tyres, very large and stiff, having a footprintwhich is narrow in the circumferential direction and elongated (i.e.wide) in the axial direction of the tyre. All these features howeverhave the opposite effect when running on snow is concerned.

The lack of side grip adversely affects the traction power on leaving abend, giving rise to loss of grip of the rear axle of the car.

In addition, traditional block patterns for snow result in high noisewhen the tyre rolls on dry and compact road surfaces, reaching peaks ofhigh intensity at given frequencies connected with the number of blocksdisposed on each circumferential row of the tread band.

The Applicant has found that these problems particularly arise onvehicles in which the geometry of the suspensions imposes rather markedcamber angles, for instance included between 0°, 5′ and 2°, typical ofthe above mentioned high performance cars. In more detail, the camberangle is the inclination of the equatorial plane of a tyre from adirection normal to the road plane. In cars with a negative camber thetyre footprint has an amplitude increasingly growing towards the axiallyinternal edge of the tyre, contrary to what happens to tyre footprintsof cars with a Positive camber.

The Applicant has further noticed that known winter tyres do not ensurethe same performance level on dry roads as that obtainable with tyresexpressly planned for use on such types of roadway.

While trying to find a solution to the problems set out hereinabove, theApplicant has perceived that the presence of transverse cutssubstantially extending over the whole axial size of the tread bandcreates a forced correlation between the number of blocks present in thedifferent circumferential rows, which greatly contributes to the originof the above described problems.

The Applicant has therefore found the possibility of achieving importantimprovements in tyre behaviour as regards most of the problems found inthe known art and correlated with side grip, handling, traction powerand braking on snow as well as in terms of noiseless running on a dryroad, through accomplishment of a tread band pattern in which the numberof blocks arranged in each circumferential row is not strictlyconditioned by the number of blocks present in other circumferentialrows, for example in the shoulder rows.

Therefore, in accordance with the present invention, it is proposed atyre for vehicle wheels comprising a tread band having a tread bandpattern defined by at least two circumferential portions disposed inaxial side by side relationship, at least one of which has a firstgeometric module repeated many times along a circumferential-extensiondirection of the tyre and comprising: a land portion or elongated ridgedelimited by two grooves oblique to the circumferential-extensiondirection and divided into a plurality of intermediate blocks withrespect to an axial-extension direction of the tread band, which arebounded by a plurality of cuts substantially transverse to the elongatedridge; at least two shoulder blocks associated with the elongated ridgeand circumferentially aligned along a side edge of the tread band anddelimited by grooves oriented transversely to the circumferentialextension of the tyre.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become more apparent from thedetailed description of a preferred but not exclusive embodiment of atyre for vehicle wheels in accordance with the present invention.

This description will be set out hereinafter with reference to theaccompanying drawings given by way of non-limiting example, in which:

FIG. 1 is a fragmentary plan view showing a tread band of a tyre made inaccordance with the present invention;

FIG. 2 shows in enlarged scale one geometric module of the tread bandpattern of a first circumferential portion of the tread band shown inFIG. 1;

FIG. 3 shows in enlarged scale a second geometric module of the treadband pattern of a second circumferential portion of the tread band ofFIG. 1;

FIG. 4 shows a second embodiment of the tread band of FIG. 1;

FIG. 5 shows a third embodiment of the tread band of FIG. 1;

FIG. 6 shows a fourth embodiment of the tread band of FIG. 1; and

FIG. 7 shows the longitudinal-section outline of a cut sectioned alongline VII-VII of FIG. 1.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring particularly to the above drawings, generally denoted at 1 isa tread band of a tyre made in accordance with the present invention;the remaining parts of the tyre are not highlighted since they can bemade in any manner convenient for a person skilled in the art.

The tread band 1 has a tread band pattern 2 defined by at least twocircumferential portions 3 a, 3 b disposed in axial side by siderelationship.

In at least one of the circumferential portions 3 a, 3 b, the tread bandpattern is substantially defined by a first geometric module 4 arepeated many times along the circumferential extension direction X ofthe tyre.

It is pointed out that by the term “geometric module” it is herein meanta predetermined shape that is repeated along the circumferentialextension X of the tyre. Geometric figures having the same shape,although with different circumferential and/or axial sizes, are at allevents ascribable to a unique geometric module. In particular, onrepeating the geometric module, different circumferential sizesfollowing each other in a predetermined sequence along thecircumferential extension of the tyre can be attributed to the shapeidentifying the module so as to distribute the rolling noise on a widerspectrum of frequencies, according to a predetermined so-called “pitchsequence”.

Advantageously, the first geometric module 4 a has at least two shoulderblocks 5 that are circumferentially aligned along a side edge 6 of thetread band 2 and bounded by grooves 7 oriented transversely to thecircumferential extension of the tyre.

The first geometric module 4 a further has an elongated ridge 8delimited between two oblique grooves 9 with respect to thecircumferential extension direction X. The elongated ridge 8 is dividedinto a plurality of intermediate blocks 10 with respect to an axialextension direction Y of the tread band 1, bounded by cuts 11substantially transverse to the elongated ridge 8.

In the embodiment shown in FIGS. 1 and 2, six intermediate blocks 10 areprovided in each elongated ridge 8. However ridges 8 with a differentnumber of blocks 10 can be made by suitably varying the sizes of theblocks 10 themselves or the length of ridge 8 in compliance with thenominal width of the tyre.

By way of example, each transverse groove 7 and each oblique groove 9has a depth P1 included between 6 mm and 10 mm, and a width L1 includedbetween 4 mm and 13 mm, measured on an outer rolling surface of thetread band 1. The depth and/or width of the transverse grooves 7 can notbe the same as that of the oblique grooves 9.

Cuts 11 have a depth P2 preferably smaller than that of grooves 7, 9 andincluded just as an indication between 2 mm and 10 mm, and a width L2included, by way of example, between 2 mm and 10 mm, and preferablylower than that of grooves 7 and 9.

In addition, to give the intermediate blocks 10 greater structuralsteadiness to the advantage of handling, running noiselessness and wearevenness, the blocks themselves can be connected with each other byreinforcing elements 12 placed in cuts 11. In more detail, taking intoaccount the longitudinal section of a cut 11, as shown in FIG. 7, eachreinforcing element can be defined by a portion of reduced deptharranged at the central region of the respective cut 11. The depth ofcut 11 at the central region can be included, by way of example, between1.5 mm and 9.5 mm.

In the embodiment herein illustrated, all intermediate blocks 10 areconnected with each other by reinforcing elements 12 but the possibilityof providing that only part of blocks 10 are connected with each otheris not excluded.

Cuts 11 transverse to the elongated ridge 8 preferably comprise firstcuts 11 a substantially perpendicular to the circumferential extension Xand second cuts 11 b substantially perpendicular to the oblique grooves9. As a matter of fact, the transverse cuts 11 have a curved shape theconcavity of which is turned in the same direction. Ascribed to each ofthem can be a median (meridian) line M₁ defined as a series of pointsspaced apart the same distance from the respective edges of the cut.

The second cuts 11 b have an inclination included between 25° and 55°with respect to the axial direction Y, wherein this inclination isrepresented by angle α₁ formed between the median line M₁ and the axialdirection Y.

Advantageously, the first cuts 11 a and second cuts 11 b are disposed inan alternate sequence along a major extension direction Z of theelongated ridge 8, so that each of the intermediate blocks 10 has asubstantially trapezoidal shape.

Transverse cuts 11 all having the same inclination may be also provided.

The oblique grooves 9 have an inclination included between 15° and 35°relative to the circumferential direction X, wherein this inclination isrepresented by angle α₂ formed between the median line M₂, spaced apartthe same distance from the edges 9 a of the oblique groove 9, and thecircumferential direction X.

The transverse grooves 7 are slightly curved and have an inclinationincluded between 75° and 105° relative to the circumferential directionX, wherein this inclination is represented by angle α₃ formed betweenthe median line M₃ as defined for the transverse cuts 11 of theelongated ridge 8, and the circumferential direction X.

In the embodiments shown the oblique grooves 9 each have an orientationconcordant with the transverse grooves 7 and run in the extension of oneof the transverse grooves 7 themselves.

In particular, the elongated ridge 8 has an axially external end 13located close to the tyre shoulder and substantially in alignment, in anaxial direction, with one of the shoulder blocks 5. The axially externalend 13 of the elongated ridge 8 is defined by an end block 14 having asubstantially trapezoidal shape.

The first geometric module 4 a further comprises an auxiliary block 15disposed circumferentially close to the axially external end 13 of theelongated ridge 8 and substantially having a trapezoidal shape.

The auxiliary block 15 is bounded by a first branch 16 and a secondbranch 17 of the oblique groove 9 each terminating at one of thetransverse grooves 7. Preferably, both the first branches 16 and thesecond branches 17 are substantially aligned with one of the transversegrooves 7, and the auxiliary block 15 is substantially aligned, in anaxial direction, with one of the shoulder blocks 5.

More specifically, the first branch 16 extending from an axiallyexternal end 18 of the oblique groove 9 delimits the end block 14 of theelongated ridge 8, on one side 16 a, and the auxiliary block 15, on theopposite side 16 b.

The second branch 17 extending from an intermediate point 19 locatedbetween the axially external end 18 and an axially internal end 20 ofthe oblique groove 9, delimits the auxiliary block 15, on one side 17 a,and the end block 14 of the adjacent elongated ridge 8, on the oppositeside 17 b.

The end block 14 and auxiliary block 15 appear as appendices of therespective shoulder blocks 5 spaced apart therefrom by a circumferentialshoulder groove 21 separating the elongated ridges 8 from the shoulderblocks themselves. The shoulder groove 21 has a width included, just asan indication, between 1.5 mm and 6 mm and a depth included, by way ofexample, between 2 mm and 10 mm, preferably smaller than that of thetransverse groove 7 over at least part of the circumferential extensionof each shoulder block 5. The first and second branches 16, 17 and therespective transverse grooves 7 open into the circumferential shouldergroove 21.

The elongated ridge 8 further has a swollen axially internal end 22 inwhich at least two centre blocks 23, 24 are defined; said blocks arecircumferentially aligned and each have a substantially trapezoidalshape.

The centre blocks 23, 24 are bounded by transverse cuts 25 converginginto a circumferential separating groove 26 interposed between thecircumferential portions 3 a, 3 b of the tread band pattern.

In particular, a first centre block 23 is separated from one of theintermediate blocks 10 by one of the second transverse cuts 11 b. Alsoassociated with the first centre block 23 is a second centre block 24separated from the first centre block 23 by one of the transverse cuts25 converging into the circumferential separating groove 26. Finally,the first centre block 23 is also delimited by one of the second centreblocks 24 which is circumferentially consecutive by means of one of thetransverse cuts 25.

Advantageously, as shown in FIGS. 1 to 4, the shoulder blocks 5 do notall have the same circumferential size C along the circumferential tyreextension. The elongated ridges 8 too have a varying transverse sizedepending on the size of the shoulder blocks 5 associated therewith.This is due to the fact that, as above mentioned, in repeating thegeometric module along the circumferential tyre extension, the moduleshape is preferably proposed again in several different forms mainlydifferentiated from each other in the size of the circumferentialextension so that at least one of the two shoulder blocks 5 associatedwith one of the elongated ridges 8 has different circumferential sizes Cwith respect to those of at least one of the two shoulder blocks 5associated with at least one of the adjacent elongated ridges 8.

Furthermore, the two shoulder blocks 5 associated with one individualelongated ridge 8 can have the same circumferential sizes C or differentcircumferential sizes C.

For example, denoted at 8 a in FIG. 1 is an elongated ridge the axiallyexternal end 13 of which is associated with a shoulder block 5 having acircumferential size C₁ greater than the circumferential size C₂ of theshoulder block 5 aligned with the auxiliary block 15 belonging to thesame geometric module. In addition, denoted at 8 b is an elongated ridgethe axially external end 13 of which is associated with a shoulder block5 having a circumferential size C₃ smaller than the circumferential sizeC₄ Of the shoulder block 5 aligned with the corresponding auxiliaryblock 15.

A further elongated ridge identified with 8 c is also provided in whichthe shoulder blocks 5 all have the same circumferential size C₅.

The tread band 1 also has a plurality of sipes 27 formed in thedifferent blocks 5, 10, 15, 23 and 24 and mainly extending in an axialdirection.

Advantageously, each sipe 27 may extend following a sawtoothed profilethe depth of which is in the range of 1.5 mm to 9.5 mm and the width ofwhich does not exceed 1 mm. Furthermore, sipes 27 are circumferentiallyspaced apart from each other by a value D included between 4 mm and 8mm.

The tread band 1 further has a plurality of notches 28 connecting sipes27. In particular, two adjacent sipes 27 are connected by at least oneconnecting notch 28 having a substantially circumferential extensionwith a depth in the range of 1 mm to 3 mm and a width in the range of 1mm to 2 mm, measured in an axial direction.

The connecting notches 28 generally do not connect more than twoconsecutive sipes 27 and do not open into the grooves 7, 9 and the cuts11 delimiting the blocks.

In more detail, each of the shoulder blocks 5 has a first series 29 ofsipes 27 disposed according to an extension substantially parallel tothe transverse grooves 7.

The intermediate blocks 10 each have a second series 30 of sipes 27disposed parallel to each other mainly in an axially-extendingdirection.

The centre blocks 23, 24 each have a third series 31 of sipes 27disposed parallel to each other mainly in an axially-extendingdirection.

Finally, the end blocks 14 and auxiliary blocks 15 each have a fourthseries 32 of sipes 27 disposed according to an extension substantiallyparallel to the transverse grooves 7.

In the embodiments shown, each of the shoulder blocks 5, end blocks 14and auxiliary blocks 15 is provided with three or four sipes 27. Each ofthe centre blocks 23, 24 has four or five sipes 27. The intermediateblocks 10 each have four sipes 27.

Advantageously, as shown in FIGS. 1 to 4, the tread band pattern 2comprises a first circumferential portion 3 a and a secondcircumferential portion 3 b disposed in side by side relationship andspaced apart from each other by the circumferential separating groove26.

Advantageously, the separating groove 26 can be spaced apart from theequatorial plane E of the tyre (FIGS. 1 and 4) towards one or the otherof the tyre shoulders, by an amount for example included between 2% and8% of the overall width of the tread band 1.

In the second circumferential portion 3 b, the tread band is defined bya second geometric module 4 b repeated many times along thecircumferential tyre extension.

In accordance with the embodiment shown in FIG. 1, the firstcircumferential portion 3 a of the tread band pattern 2 has the samestructure as hitherto described whereas the second geometric module 4 bof the second circumferential portion 3 b comprises two shoulder blocks34 and four inner blocks 35 (FIG. 3).

Repeating the second geometric module 4 b along the circumferentialextension X gives origin to a plurality of shoulder blocks 34 arrangedalong a single row, and to a plurality of inner blocks 35.

Also the shoulder blocks 34 and inner blocks 35 of the second geometricmodule 4 b in accordance with the embodiments shown in FIGS. 1, 3 and 4do not all have the same circumferential size C along the tyreextension.

The shoulder blocks 34 of the second circumferential portion 3 b inaccordance with the preferred embodiment are circumferentially alignedalong a side edge 36 of the tread band 1, axially opposite to the sideedge 6 of the first circumferential portion 3 a, and confined by grooves37 oriented transversely of the circumferential tyre extension.

More specifically, the transverse grooves 37 are slightly curved andhave an inclination included between 75° and 105° with respect to thecircumferential direction X, wherein said inclination is represented byangle α₄ formed between the medial line M₄, as defined for thetransverse cuts 11 of the elongated ridge 8, and the circumferentialdirection X itself.

The inner blocks 35 are distributed along at least one firstcircumferential row 38 separated from the shoulder blocks 34 of thesecond circumferential portion 3 b by a circumferential shoulder groove39 and are delimited by grooves 40 oriented transversely to thecircumferential tyre extension.

Preferably, the second circumferential portion 3 b of the tread bandpattern 2 further comprises a second circumferential row 41 of innerblocks 35 disposed in axial side by side relationship with the first row38 and separated therefrom by a circumferential groove 42.

In further embodiments not shown, the tyre can be provided with morethan two circumferential rows of inner blocks 35, for example along thenominal chord of the tyre itself.

Just as an indication, grooves 37, 39, 40, 42 of the secondcircumferential portion 3 b and the separating groove 26 do notnecessarily have the same depth P3, said depth being preferably includedbetween 6 mm and 10 mm.

The inner blocks 35 of each row 38, 41 can advantageously be connectedwith each other by reinforcing elements 12 similar to the reinforcingelements 12 used for the intermediate blocks 10 of the elongated ridges8.

In addition, the transverse grooves 37 of the shoulder blocks 34, thecircumferential grooves 39, 42 and separating groove 26 do notnecessarily have the same width L3, said width being preferably includedbetween 4 mm and 13 mm, measured on an outer rolling surface of thetread band 1.

Finally, the transverse grooves 40 of the inner blocks 35 have a widthL4 included between 2 mm and 10 mm, generally smaller than the width L3typical of grooves 37 in the shoulder blocks 34, as well as of thecircumferential grooves 39, 42 and separating groove 26. Advantageously,the transverse grooves 40 bounding the inner blocks 35 of the first row38 are circumferentially offset with respect to the transverse grooves37 of the shoulder blocks 34 of the second circumferential portion 3 band, where the second row 41 is also provided, with respect to thetransverse grooves 40 bounding the inner blocks 35 of the second row 41.

Between the transverse grooves 40 delimiting the inner blocks 35 areprovided first grooves 40 a that are inclined to the axial direction Yand second grooves 40 b substantially perpendicular to thecircumferential tyre extension. The first grooves 40 a and secondgrooves 40 b are disposed in an alternate sequence along the respectivecircumferential row 38, 41, so as to give the inner blocks 35 asubstantially trapezoidal shape.

More specifically, the transverse grooves 40 have a curved shape theconcavity of which is turned in the same direction. A median linedefined as the series of points spaced apart the same distance from therespective edges of the groove can be ascribed to each of said grooves.

The first grooves 40 a are inclined to the axial direction Y by an angleincluded between 25° and 55°, wherein said inclination is represented byangle α₅ formed between the median line M₅ and the axial direction Y.

The second grooves 40 b too are inclined to the axial direction Y by anangle included between 5° and 20°, wherein this inclination isrepresented by angle α₆ formed between the median line M₆ and the axialdirection Y.

Preferably, the first grooves 40 a delimiting the inner blocks 35 of thefirst circumferential row 38 and the first grooves 40 a delimiting theinner blocks 35 of the second circumferential row 41 are parallel toeach other.

Alternatively, according to an embodiment not shown, the first grooves40 a delimiting the inner blocks 35 of the first circumferential row 38and the first grooves 40 a delimiting the inner blocks 35 of the secondcircumferential row 41 symmetrically converge towards thecircumferential groove 42 separating the first row 38 from the secondrow 41.

The possibility of providing grooves 40 all having the same inclinationis not to be excluded.

Advantageously, the inner blocks 35 and shoulder blocks 34 have theirlongitudinal sides 35 a, 34 a, i.e. those sides substantially orientedin the circumferential direction X, inclined to the circumferentialdirection X itself by an angle α₇ included between 1° and 5° so as togenerate widened portions 45 in the circumferential grooves 39, 41belonging to the second circumferential portion 3 b and in theseparating groove 26. The transverse grooves 40 delimiting the innerblocks 35 open into these widened portions 45. In addition, to increaseamplitude of the widened portions 45, at least one of the corners of theinner blocks 35 facing said portion 45 is rounded off at 46 so as tooffer more room for snow entrapping.

In accordance with the embodiment shown in FIG. 1, the transversegrooves 37 in the shoulder blocks 34 of the second circumferentialportion 3 b and the transverse grooves 7 of the shoulder blocks 5 of thefirst circumferential portion 3 a are substantially parallel, to giveorigin to a tyre of the asymmetric and non-directional type.

Alternatively, according to a second embodiment shown in FIG. 4, thetransverse grooves 37 of the shoulder blocks 34 of the secondcircumferential portion 3 b and the transverse grooves 7 of the shoulderblocks 5 of the first circumferential portion 3 a converge towards eachother, to give origin to a tyre of the asymmetric-directional type.

In both the embodiments shown in FIGS. 1 and 4 the secondcircumferential portion 3 b too is provided with a plurality of sipes 27extending according to a sawtoothed profile and mutually connected by aplurality of notches 28 in the same manner as described for the firstgeometric module 4 a. Sipes 27 of the second circumferential portion 3 bhave a depth included between 1.5 mm and 9.5 mm and a width notexceeding 1 mm.

In particular, each of the shoulder blocks 34 of the secondcircumferential portion 3 b has a fifth series 47 of sipes 27 disposedsubstantially parallel to the transverse grooves 37 delimiting theshoulder blocks 34 themselves. The shoulder blocks 34 of the secondcircumferential portion 3 b as well have circumferential sizes differentfrom each other and are provided with three or four sipes 27 dependingon their circumferential size.

In addition, advantageously, each of the inner blocks 35 of the firstcircumferential row 38 has a sixth series 48 of sipes 27 disposedparallel to each other and the extension of which is oblique to theaxial direction Y and parallel to the first grooves 40 a in the innerblocks 35 of the first circumferential row 38.

Preferably, as shown in FIGS. 1, 3 and 4, the first row 38 has innerblocks 35 with five sipes 27, and inner blocks 35 with four sipes 27.

The inner blocks 35 of the second circumferential row 41 each have aseventh series 49 of sipes 27 disposed parallel to each other and havingan extension oblique to the axial direction Y and parallel to the firstgrooves 40 a in the inner blocks 35 of the second circumferential row41.

The second row 41 too has inner blocks 35 with five sipes 27, and innerblocks 35 with four sipes 27.

Finally, as can be viewed from FIGS. 1 and 4, the number of the shoulderblocks 34 of the second circumferential portion 3 b is the same as thenumber of the inner blocks 35 of the first circumferential row 38 and asthe number of the inner blocks 35 of the second circumferential row 41,and is twice the number of the elongated ridges 8 of the firstcircumferential portion 3 a.

In accordance with a third embodiment and a fourth embodiment, shown inFIGS. 5 and 6 respectively, the second geometric module 4 b of thesecond circumferential portion 3 b of the tread band pattern 2 issimilar in structure to the geometric module 4 a of the first portion 3a.

In particular, the second geometric module 4 b too comprises at leasttwo shoulder blocks 5 circumferentially aligned along a side edge 36 ofthe tread band 1 axially opposite to the side edge 6 belonging to thefirst geometric module 4 a and bounded by grooves 7 orientedtransversely to the circumferential tyre extension. The second geometricmodule 4 b further comprises an elongated ridge 8 delimited by twooblique grooves 9 with respect to the circumferential extensiondirection X and divided into a plurality of blocks 10 disposed at anintermediate position in the axial extension of the tread band 1 anddelimited by a plurality of cuts 11 substantially transverse to theelongated ridge 8.

In the third embodiment shown in FIG. 5, the oblique grooves 9 of thesecond geometric module 4 b converge towards the oblique grooves 9 ofthe first geometric module 4 a to form a tyre of the directional type.In the particular embodiment shown, the second geometric module 4 b issymmetric with the first geometric module 4 a with respect to theequatorial plane E of the tyre and is also circumferentially offsetrelative to the first geometric module itself.

In a fourth embodiment shown in FIG. 6, the oblique grooves 9 of thesecond geometric module 4 b are substantially parallel to the obliquegrooves 9 of the first geometric module 4 a, to create a tyre of thesymmetric type.

In the particular embodiment shown, the second geometric module 4 b isidentical to the first geometric module 4 a, but rotated of 180° in theplane of the figure and circumferentially offset relative to the firstgeometric module itself.

In further embodiments not shown the geometric modules 4 a, 4 b of thetwo, circumferential portions 3 a, 3 b, while having the same structure,can advantageously have different sizes, particularly in relation to thelength of the elongated ridges 8.

The present invention thus achieves the intended purposes.

The innovative expedients proposed by the invention, in fact, give riseto important improvements in terms of side grip of the tyre on roadwaysof reduced compactness, in particular on snow-covered surfaces, togetherwith excellent qualities in terms of traction power and braking due inparticular to the conformation of the first geometric module 4 a adoptedfor the circumferential portion 3 a shown in FIG. 1, and to the synergicco-operation with the second geometric module 4 b.

In fact, due to the presence of cuts and grooves transverse to the axialdirection, a remarkable surface for ground contact and snow accumulationis offered when the tyre is submitted to side forces. The presence ofsawtoothed sipes also helps in achieving this result. Simultaneously,the transverse cuts and transverse grooves work, together with the cutsparallel to the axial direction, in order to supply traction power andgrip on braking.

In addition, the oblique grooves ensure an efficient water ejection thathelps in avoiding occurrence of the dangerous phenomenon known as“aquaplane”.

It should be also understood that distribution of the blocks internal tothe elongated ridges and of the shoulder blocks, as well as theinclination of same relative to the circumferential direction give riseto a noise spectrum distributed over a wide frequency band and ofreduced intensity, thereby greatly reducing the rolling noise felt bothinternally and externally of the car. In fact, the number of pointsbelonging to the edges of the blocks simultaneously coming into contactwith the ground during rolling of the tyre is very reduced.

Simultaneously, the particular pattern of the first geometric module 4 aat all events ensures a large contact surface between tyre and asphaltand consequently a performance level on dry roadways comparable withthat ensured by a tread pattern expressly designed for such conditions.

Referring particularly to the embodiment of FIG. 1 and to the secondembodiment of FIG. 2, differentiation of the two circumferentialportions with the inner portion characterised by elongated ridgesenables an optimised tyre for high performance cars with negative camberto be obtained. In fact, the two portions embody different features and,being applied simultaneously, ensure an optimal performance in all testsfor tyre evaluation.

The outer portion works principally during changes of direction onsnow-covered roadways, in particular on leaving a bend, since the snowbears against the shoulder blocks and inner blocks and is entrapped intothe labyrinth path generated by them and into the greatly inclinedsipes. The inner portion which, as already specified, represents thelargest part of the footprint area, ensures a good behaviour on dry orwet roads as well.

Finally, distribution of the cuts and grooves following differentinclinations over the whole extension of the tread band enables tendencyof the tyre during rolling to rotate about an axis orthogonal to therest surface to be minimised, which effect is known in the specificfield as “torque steer”.

In confirmation of the above mentioned advantages, two tables arereproduced hereinafter which relate to comparison tests between the tyre(P) of the present invention and three different tyres of the known art(Pr, P1, P2) having the same sizes 205/55 R16. Tyre Pr is a referencetyre produced by the Applicant and has the same structure and elastomercomposition, in the different component elements thereof, of theinventive tyre. Tyres P1 and P2 are two reference tyres representing thetwo best tyres available from competitor firms and presently on themarket.

The tyres were tested both on a snow-covered roadway and a dry road,using the same motor-vehicle and under the same environmentalconditions. In particular, tests were conducted utilising a BMW 328i car(rear-wheel drive) and an Audi A3 1.8T car (front-wheel drive).

The values reproduced in the following tables represent a mean valuebetween those obtained in several test sessions (5-6 tests, for example)using both the above mentioned cars.

In particular, tyres were submitted to instrument tests on traction,braking and slalom on a snow-covered roadway; to braking tests on a dryroadway; to noise tests; to aquaplane tests on a bend and on a straightstretch.

The above tyres were further submitted to subjective tests on traction,braking and handling on a snow-covered roadway; to handling tests on adry and a wet roadway; and to noise tests, writing down the testdrivers' subjective evaluations (expressed through a point system).

Table 1 refers to instrument tests, whereas Table 2 reproduces the testdrivers' subjective evaluations.

The traction tests on a snow-covered roadway were conducted carrying outfirst-gear standing starts. With reference to Table 1, the maximumtraction force of tyres P, P1, P2 was measured and expressed as apercentage of the maximum traction force of the reference tyre Pr.

Braking tests on a snow-covered roadway were carried out withdeceleration from 50 to 5 km/h by using both the antilock braking system(ABS) and locked-wheel system.

Braking tests on dry asphalt were conducted with decelerations from 100to 5 km/h by using the ABS system.

The average deceleration of tyres P, P1, P2 was measured and expressedas a percentage of the maximum deceleration of the reference tyre Pr.

The slalom test on a snow-covered roadway was conducted between tentraffic cones placed at a distance of eighteen meters from each otherand at a speed included between 35 and 45 km/h; the maximum sideacceleration of tyres P, P1, P2 during the slalom test was measured andexpressed as a percentage of the maximum acceleration of the referencetyre Pr.

The aquaplane test on a straight stretch was carried out on a smoothasphalt stretch (100 m long, for example) covered with a water layer ofconstant depth (7 mm). The water layer was restored after each passageso as to ensure the same conditions during each test. The test wasconducted by making the vehicle to enter the asphalt stretch at aconstant speed (70 km/h, for example) under optimal grip conditions andby progressively accelerating the vehicle until reaching conditions ofcomplete grip loss. During the test the speed at which all wheels losegrip was measured and this speed was expressed as a percentage of themaximum speed of the reference tyre Pr.

The aquaplane test on a bend was carried out on a curvilinear path ofconstant radius (of 100 m) the final stretch of which (over a portion 20m long, for example) was covered with a water layer of constant depth (7mm deep). The test was conducted at a constant speed and repeated fordifferent speed values. The maximum speed and maximum acceleration ofthe car on the bend were measured before grip loss and these values wereexpressed as a percentage of the maximum speed and maximum accelerationof the reference tyre Pr.

The outdoor noise test (the term “outdoor” being used to distinguish itfrom the indoor noise test carried out in a semi-anechoic chamber) wasconducted in order to evaluate both the internal noise of the car andthe external noise of same.

In order to evaluate the internal noise of the car, the test consistedin driving the car at a predetermined constant speed and subsequentlymaking the car to run a straight stretch with a switched-off engine andin neutral (this test is called “coast by noise”). The test is repeateddriving the car at different speeds. When cars were run on this straightstretch with a switched-off engine and in neutral, the internal noise ofthe car was instrumentally measured by use of a so-called “acoustichead” simulating the driver/passenger position within the car by meansof microphones positioned at the ear height. The test further consistedin a subjective evaluation (expressed through a point system) carriedout by the test driver having the task of evaluating the noise levelperceived within the car.

This test was further conducted making the car to travel over saidstraight stretch at constant speed, without switching the engine off. Inaddition, this test was repeated on different asphalt typologies.

In order to evaluate the noise external to the car, the test consistedin causing the car to run over a straight stretch provided withmicrophones disposed on opposite sides of said stretch.

The test was conducted following two different modalities: a) imposingan acceleration to the car while said car was covering the abovementioned stretch (this test is called “pass by noise”); b) bringing thevehicle to a constant speed, by switching the engine off and putting itin neutral at the above mentioned straight stretch.

The handling tests were conducted on a track and the test driversimulated some characteristic manoeuvring (change of lane, entering abend, leaving a bend, for example) carried out at constant speed, inacceleration and in deceleration. Then test driver judged the tyrebehaviour and assigned a score depending on the tyre performance duringsaid manoeuvring.

The average scores given by several test drivers to the differentperformance tests taken into account are reproduced in Table 2.

In the tables it is possible to see that the tyre of the presentinvention has higher, scores than the tyres of the known art.

The values reproduced in the tables are expressed in relation to thevalue of 100 given to the reference tyre Pr.

TABLE 1 Instrument tests P Pr P1 P2 Traction on snow 105 100 101 98Braking on snow 102 100 98 100 Slalom on snow 106 100 100 97 Braking ondry asphalt 101 100 101 100 Aquaplane on a bend 104 100 101 98 Aquaplanein straight 103 100 102 97 stretch Outdoor noise 107 100 95 98 (internalnoise) Outdoor noise 105 100 98 100 (external noise)

TABLE 2 Subjective tests P Pr P1 P2 Traction on snow 108 100 101 99Braking on snow 103 100 98 101 Handling on snow 108 100 102 102 Handlingon a dry 105 100 98 100 roadway Handling on a wet 105 100 99 98 roadwayOutdoor noise on 108 100 96 99 smooth/coarse asphalt

The invention claimed is:
 1. A tyre for a vehicle wheel, comprising: a tread band; wherein the tread band comprises a tread-band pattern, wherein the tread-band pattern comprises at least two circumferential portions, wherein at least one of the circumferential portions comprises a first geometric module, wherein the first geometric module comprises: an elongated ridge; an end block; an auxiliary block; and at least two shoulder blocks; wherein the at least two circumferential portions are disposed in an axial side-by-side relationship; wherein the first geometric module is repeated along a circumferential extension direction of the tyre, wherein the elongated ridge is bounded by two oblique grooves oriented to be oblique to the circumferential extension direction, wherein the elongated ridge is divided into a plurality of intermediate blocks with respect to an axial extension direction of the tread band, wherein the intermediate blocks are bounded by a plurality of cuts substantially transverse to the elongated ridge; wherein the end block defines an axially external end of the elongated ridge, substantially in axial alignment with one of said at least two shoulder blocks; wherein the auxiliary block is disposed circumferentially close to the end block, substantially in axial alignment with another of said at least two shoulder blocks and wherein the auxiliary block is separated from two intermediate blocks of the elongated ridge by one of the oblique grooves such that the auxiliary block is axially between the two intermediate blocks and the another of said at least two shoulder blocks; wherein the at least two shoulder blocks are associated with the elongated ridge, wherein the at least two shoulder blocks are circumferentially aligned along a side edge of the tread band, and wherein the at least two shoulder blocks are bounded by substantially transverse grooves oriented substantially transversely to the circumferential extension direction.
 2. The tyre of claim 1, further comprising: at least one circumferential groove separating the at least two circumferential portions.
 3. The tyre of claim 2, wherein the at least one circumferential groove separating the at least two circumferential portions is spaced apart from an equatorial plane of the tyre.
 4. The tyre of claim 1, wherein the oblique grooves have an inclination included between 15° and 35° relative to the circumferential extension direction.
 5. The tyre of claim 1, wherein the substantially transverse grooves have an inclination included between 75° and 105° relative to the circumferential extension direction.
 6. The tyre of claim 1, wherein the elongated ridge comprises a swollen axially internal end, comprising: at least two center blocks circumferentially aligned with each other.
 7. The tyre of claim 6, wherein each center block comprises a substantially trapezoidal shape.
 8. The tyre of claim 6, wherein the center blocks are bounded by substantially transverse cuts converging into a circumferential separating groove interposed between the at least two circumferential portions.
 9. The tyre of claim 1, wherein the at least two shoulder blocks comprise a same circumferential size.
 10. The tyre of claim 1, wherein the at least two shoulder blocks comprise different circumferential sizes.
 11. The tyre of claim 1, wherein the at least two shoulder blocks associated with a first elongated ridge comprise different circumferential sizes than the at least two shoulder blocks associated with a second elongated ridge circumferentially adjacent to the first elongated ridge.
 12. The tyre of claim 1, wherein the end block comprises a substantially trapezoidal shape.
 13. The tyre of claim 1, wherein the auxiliary block is bounded by first and second branches of one of the oblique grooves, and wherein each branch opens into one of the substantially transverse grooves.
 14. The tyre of claim 13, wherein each of the first and second branches is substantially in alignment with one of the substantially transverse grooves.
 15. The tyre of claim 1, wherein the auxiliary block comprises a substantially trapezoidal shape.
 16. The tyre of claim 12, wherein the shoulder block substantially in axial alignment with the axially external end comprises a circumferential size greater than a circumferential size of the shoulder block substantially in axial alignment with the auxiliary block.
 17. The tyre of claim 12, wherein the shoulder block substantially in axial alignment with the axially external end comprises a circumferential size smaller than a circumferential size of the shoulder block substantially in axial alignment with the auxiliary block.
 18. The tyre of claim 1, wherein the tread-band pattern further comprises: a plurality of sipes.
 19. The tyre of claim 18, wherein the sipes are formed on the first geometric module in a mainly axial extension.
 20. The tyre of claim 19, wherein each sipe comprises a sawtoothed profile.
 21. The tyre of claim 19, wherein the tread-band pattern further comprises: a plurality of connecting notches between the sipes.
 22. The tyre of claim 1, wherein each shoulder block comprises: a first series of sipes; wherein the sipes of the first series comprise a sawtoothed profile, and wherein the sipes of the first series are disposed parallel to each other according to an extension substantially parallel to the substantially transverse grooves.
 23. The tyre of claim 1, wherein each intermediate block comprises: a second series of sipes; wherein the sipes of the second series comprise a sawtoothed profile, and wherein the sipes of the second series are disposed parallel to each other in a mainly axial extension.
 24. The tyre of claim 6, wherein each center block comprises: a third series of sipes; wherein the sipes of the third series comprise a sawtoothed profile, and wherein the sipes of the third series are disposed parallel to each other in a mainly axial extension.
 25. The tyre of claim 1, wherein each end block and each auxiliary block comprises: a fourth series of sipes; wherein the sipes of the fourth series comprise a sawtoothed profile, and wherein the sipes of the fourth series are disposed parallel to each other according to an extension substantially parallel to the substantially transverse grooves.
 26. The tyre of claim 1, wherein the oblique grooves each run in an extension of one of the substantially transverse grooves. 